This invention relates to dipole antennas and more particularly to a shortened aperture, center fed dipole antenna that may be made flexible enough to be efficiently packaged for storing and erecting the antenna.
It is desirable in various applications that the physical length of a dipole antenna to be employed be shortened, for example, due to space requirements or other physical constraints. It is also desirable in many applications that a dipole antenna be flexible enough to be wrapped around a drum or the like for storing. In the prior art types of shortened aperture, center fed dipoles, one or more of the antenna radiating elements includes a coil or such loading means at or near the center feed point. This loading coil near the center feed point causes the magnitude of the antenna current to rapidly drop to essentially zero, resulting in the performance of the prior art shortened aperture dipole antenna to be substantially below that of the standard dipole.
According to the present invention, a shortened aperture, center fed dipole antenna system is provided by a coaxial transmission line, a radiator element connected to the inner conductor of the coaxial transmission line, and a second radiator element including the combination of a hollow conductor cylinder, coaxial with the coaxial transmission line, and a coil. One end of the conductive cylinder, which is substantially less than one quarter wavelength in physical length at the center operating frequency of the antenna, is coupled to the outer conductor of the coaxial transmission line, and the remote end of the cylinder is coupled to the coil.